In the field of semiconductor device manufacturing, active semiconductor devices such as, for example, transistors are generally manufactured or fabricated through processes commonly known as front end of line (FEOL) technologies. A transistor may be, for example, a field-effect-transistor (FET) and may be more specifically a complementary metal-oxide-semiconductor (CMOS) FET. A FET may also be a p-type dopant doped PFET or an n-type dopant doped NFET. Recently, high-k metal gate (HKMG) semiconductor transistors have been introduced because of their superior performance over conventional poly-based CMOS-FET. In addition, a replacement metal gate (RMG) process has been developed to further enhance the performance of HKMG transistors.
Generally, after structure of a transistor is formed, conductive contacts are formed to connect to source, drain, and/or gate of the transistor to make the transistor fully functional. With the continuous scaling down in device dimension in integrated circuitry, real estate for forming corresponding contacts is also becoming smaller and smaller. As a result, contacts that are borderless to gate, which generally requires less real estate and have been used for a while in dynamic random access memory (DRAM), are making their way into logic structures such as transistors.
To form borderless contacts for a transistor manufactured through a non-replacement metal gate (non-RMG) process, normally a HfO2 layer or other types of highly RIE (reactive-ion-etching) resistant etch-stop layer is formed or deposited to cover the gate stack of the transistor before depositing the CA inter-layer dielectric. Metal contacts are then formed next to the etch-stop layer to be borderless to the gate. However, despite demonstrated feasibility of the above approach for transistors made by various non-RMG processes, technical difficulties have been met in trying to apply the above approach to transistors manufactured by a RMG process.